Mixing Assisted Direct Formation of Isotactic Poly(1-butene) Form I′ Crystals from Blend Melt of Isotactic Poly(1-butene)/Polypropylene

The influence of mixing of iPB-1/iPP blend on the polymorphism of iPB-1 under processing-relevant conditions is studied with emphasis on "the competition between the thermodynamically stable form I' crystal and the kinetically favored form II. In situ optical microscopy measurements reveal that the upper critical solution temperature (UCST) of iPB-1/iPP blend locates in the range of 180-200 degrees C. Unexpectedly, by quenching mixed iPB-1/iPP melt down to temperatures below UCST and melting point, form I/I' can be produced directly which is further identified as form I' by temperature dependent WAXS and DSC. The formation of form I' is promoted by increasing the annealing time above UCST, while is suppresses by raising the quenching temperature. In addition, the crystallization of iPP also displays a similar trend as iPB-1 does. The correlated crystallization of each constituent with dependence on the initial mixing degree suggests that the crystallization behavior of the binary blends is determined by the interplay between simultaneous processes concomitant with the liquid-solid transition. The experimental results reveal the possibility to modify the crystallization pathway of iPB-1 in iPB-1/iPP blend through the mixing degree which is initially controlled by annealing but is subject to evolve during the subsequent thermal treatment. Possible mechanisms are discussed including the roles of phase separation and concentration fluctuation in crystallization.